1. Field of the Invention
The present invention relates to a fuel feeding device used for an in-cylinder injection type engine and is particularly related to a fuel feeding device adapted for reducing the power of pump for pressurizing the fuel to a high pressure.
2. Description of the Prior Art
A Diesel engine is widely known as an engine of a type with fuel injected within a cylinder called an in-cylinder fuel injection type engine or direct fuel injection type engine, but recently for a spark ignition type engine (gasoline engine) too, the in-cylinder fuel injection type is proposed. An ability to inject fuel with a sufficiently high pressure is required for such an in-cylinder fuel injection type engine.
FIG. 5 shows a fundamental arrangement of a conventional fuel feeding device wherein the fuel which is pressurized to a low pressure by a low pressure fuel pump 2 is regulated to a predetermined low pressure by a low pressure regulator 2 and fed to the pumping element 20A of a high pressure pump 20 from a low pressure fuel passage 8. The pumping element 20A pressurizes the fuel mentioned above to a high pressure and delivers it to a high pressure fuel passage 9. This high pressure fuel is regulated to a predetermined high pressure by a high pressure regulator 11 provided in the high pressure fuel passage 9 and is injected with predetermined timing into respective combustion chambers 22 of engine 21 after being conveyed to a delivery pipe 6 as shown by FIG. 6. Now, part of the fuel flowing through the high pressure fuel passage 9 is returned back to a fuel tank 1 through a drain passage 13 of the high pressure regulator. Up and down motion of piston of the engine 21 is transmitted to the pumping element 20A through a camshaft 25 and this transmitted motion drives an unshown piston thereby pressurizing the fuel which is sucked into the high pressure pump 20.
Since the pumping element 20A of the fuel feeding device mentioned above drives the pump proportionally to the revolution number of the camshaft 25 of the engine 21, disregarding loss, fuel having a volume proportional to the engine rotation number is pressurized and delivered. Accordingly, the pumping element 20A pressurizes and delivers the same amount of fuel regardless of whether the amount of flow required by the engine is large or small. As a result, a large amount of fuel which is already pressurized to a high pressure is obliged to be returned back to the tank 1 from the drain passage 13 of the high pressure regulator even when the amount of fuel required by the engine is small, and thus particularly during a low loading operation there gives rise to a problem of producing a large power loss of the pump.
Also an engine, which exhibits a large change in the amount of fuel which is required depending on engine load as is seen in a lean burn engine and an engine with a turbo changer has a large power loss resulting in a degradation in fuel consumption. The present invention was made to overcome problems posed in the conventional arts as above. The object of the present invention is to provide a fuel feeding device which reduces engine load by suppressing power of pump for pressurizing fuel to a minimum and thus improving the fuel consumption performance.